See video example here: Watch Video on YouTube

My problem is that, in pose mode, when I'm in the Action Editor, the initial pose of the bone (that controls the lower cylinder of the excavator/construction vehicle) is off. It's not what the keyframe has it set as. Attempting to rotate the bone or move forward in the timeline, however, puts the bone back to its proper rotation. It's only when switching between Actions that this off-rotation issue appears. The problem is the issue is continuing into Unity, the game development program, and messing up the animations. My expected behavior of the bone is that it wouldn't glitch on the 1st frame of the Action when I switch between actions.

Here is a screenshot of the TrackTo constraint I have on this bone, targeting an object above it near the upper-cylinder:

enter image description here

Here's what the bone & cylinder should look like from starting frame: enter image description here

Here's what it actually looks like when I switch between Actions (this glitch also carries into Unity): enter image description here

Does anyone know how I can fix this problem? Any help would be greatly appreciated. Thank you!

  • $\begingroup$ could you please provide a .blend file to be able to help you? $\endgroup$
    – Tak
    Jan 11, 2017 at 0:56
  • $\begingroup$ Is the geometry the TrackTo bone is constrained to also a child of the armature? Even though your idea makes sense, Blender might look at that as a circular dependency. ie) Armature [object level] -> Geometry [what the trackto bone is aimed at] -> Armature (trackto bone) $\endgroup$ Jan 11, 2017 at 1:18
  • $\begingroup$ If that's the case, try making the bone for the bone cylinder to TrackTo instead. $\endgroup$ Jan 11, 2017 at 1:22
  • $\begingroup$ @Tak, here's a link to the .blend file you can download via Dropbox: dropbox.com/s/ksvd7i9u5twp1mz/…. $\endgroup$
    – Jesse
    Jan 11, 2017 at 18:18
  • $\begingroup$ @MikeBelanger, thanks for the feedback. Yes, I believe the geometry the trackto bone is constrained to is also a child -- I could be creating a circular dependency. I'll look into that today and see if some modifications to the parent hierarchy fixes it. $\endgroup$
    – Jesse
    Jan 11, 2017 at 18:20

1 Answer 1


Thanks to comments in the original post, I was able to find the problem and create a fix.

THE PROBLEM: In this case, the bone with the TrackTo constraint was targeting a mesh object (a cylinder) which was a child of the armature, creating a circular dependency and producing the error I was experiencing.

THE FIX: Positioned in the same place as the cylinder that was being targeted is another bone controlling the upper part of the excavator mechanism. I changed the target of the TrackTo constraint to that bone above it, thus eliminating the circular dependency. Now, even from frame one, the rotation of the bone with the TrackTo constraint is right where it is supposed to be.

Thanks again to everyone for their help!


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .